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The Aperture Science Handheld Portal Device, originally marketed in the 1950s as an Aperture Science Portable Quantum Tunneling Device, also commonly known as a Portal Gun or by its acronym, "ASHPD", is an experimental tool used to create two portals through which objects can pass.

The ASHPD is a hand-held device which has the ability to manufacture two linked portals. No matter the distance between them, any object which passes through one portal will emerge from the other and vice versa instantaneously. The portals can be placed on almost any surface which is flat and large enough to accommodate them. Moving objects, or certain types of surfaces, will prevent the formation of a portal. Material Emancipation Grills will block any attempt to shoot portals through them, as well as reset any active portals should the ASHPD pass through it.

The ASHPD is held with a hand behind the weapon, holding the handle/trigger, while the other hand supports the barrel. A sprite in the small hole on the top of the ASHPD and a sprite in its glass tube have the color of the last shot portal. It has two triggers, one for each of its two portals.

When the ASHPD is fired, a burst of colored energy is emitted from the barrel, corresponding to the colored portal it is intended to create. Upon striking the targeted surface, a portal is formed, surrounded by a colored ring. If the surface cannot accommodate a portal for whatever reason, the shot will dissipate in a shower of colored particles. If one portal is shot into its opposite, the portal will be formed next to the first one, assuming the surface has enough room for it to form; otherwise, it will dissipate as normal. The device can only create two portals at a time. If a third is fired, the other of its type will be automatically closed and a new link will be formed.

The portals fired by the ASHPD each have a distinct color. Chell's ASHPD uses light blue and light orange portals. ATLAS and P-body each use a variant on those two colors; ATLAS uses light blue and purple portals, while P-body uses light orange and red portals.

The ASHPD also has a zero-point energy field manipulator, similar to the Gravity Gun but far weaker. It can pick up objects, but only those directly in front of it. If the space between the object and the ASHPD is interrupted by a solid object, there is a chance that the object will be dropped, which can sometimes occur when travelling through portals at high velocity and the object accidentally hits the edge of the portal or another object in the surrounding area. It also cannot punt them as the Gravity Gun can, so the only way to throw the object is to physically swing the ASHPD itself, which can at best send the object a few meters away. It cannot catch Aperture Science High Energy Pellets, the equivalent of CombineEnergy Balls, due to the weaker manipulator. Items picked up with the ASHPD's manipulator can be carried though portals, which proves to be very useful in several test chambers.

During Portal, Chell first acquires the ASHPD in Test Chamber 02; it fires only blue portals. It is later upgraded in Test Chamber 11 to fire the orange portals as well (while another model is found there, it actually consists of an upgrade to the current model, as said by GLaDOS). When each of the two versions of the gun are found, they are seen placed on a pedestal in the middle of a Test Chamber. The pedestal is constantly turning on itself, and the ASHPD shoots a portal each time it faces one of the four walls of the room it is in. Chell has to use the non-player controlled gun to complete the Test Chambers and once done acquires the initial ASHPD and later its upgrade. Currently it is not known how the two single ASHPDs are combined into one to result in a "modified" single gun.

In Portal 2, Chell again finds only a single-portal ASHPD near the start of the game. It appears to have been hidden in a Ratman den in the ruined Test Chamber 02 by Doug Rattmann. After GlaDOS is awakened, she loses this one. It falls on the floor in GLaDOS's chamber and is presumably retrieved by GLaDOS. GLaDOS drops her into the furnace, where a fully-functional ASHPD is waiting. Chell loses her ASHPD in the final conflict against Wheatley. When she creates a portal on the moon, the ASHPD is one of the first things sucked through. ATLAS and P-body are provided with fully-functional ASHPDs at the start of their testing.

Chell going through her own portals. The blue is on the ceiling, the orange on the floor. When properly placed, Chell can infinitely fall downwards through the portals.

The ASHPD cannot create portals on every surface. It will not work on certain tiled floors, metal, any kind of prop, doors or windows. However, it will work on security cameras, detaching them and making them fall on the ground. When shooting a portal on an unauthorized surface, the weapon's ray will bounce off and be turned into blue or orange particles that shortly disappear. This constraint was added to make puzzles deeper than merely teleporting to the exit. The surfaces a portal can be created on are the white tiles found in many areas or surfaces covered in conversion gel, which is made of ground up moon rocks.[2] Portals can also be formed on the moon itself.
With the noted exception of cameras, a portal is incapable of causing physical damage to either humans or objects. If a portal is closed while something is between it and the destination, the object will automatically be pushed out of one or the other, depending on which one the object is closer to. There are a few instances where the player can use portals to kill themselves, but this is likely an unintentional oversight.

The oval-shaped crosshair/reticle of the ASHPD indicates useful information pertaining to the portals. It first starts with a completely blue crosshair, as the first acquired ASHPD can only shoot blue portals. Later, when the ASHPD is upgraded to shoot orange portals, the crosshair is cut in two parts, blue and orange. In Portal, a smaller oval appears next to the side that has been most recently fired, and when the ASHPD is held in front of a surface where portals cannot be shot, only the outlines of the two oval elements are seen. A filled-in outline indicates a suitable surface. In Portal 2 the smaller oval does not exist, and the two oval elements fill when a portal has been fired.

Shooting an orange portal on an existing blue portal (or vice versa) will create the portal right next to it, if the room available allows it.

An Aperture Science Material Emancipation Grill will "reboot" any portal created by the ASHPD. In this way, the Test Subject starts each new Test Chamber with a "clean" portal network, and must use their assets properly to complete the chamber. They also appear within several chambers, forcing the Test Subject to find a way to work around them to complete an otherwise simple task.

The various Test Chambers require the use of several portal creating techniques, where the ASHPD and momentum play a pivotal part:

The most basic technique is "Flinging," whereby one transforms downward momentum into forward momentum by means of cleverly placed portals. This is mainly used to clear large gaps or obstacles when more orthodox means, such as stairs or lifts, are not available. The concept simply requires to place one portal facing outward on a high wall across from the area that one wishes to fly over. Meanwhile, the second portal is placed in a nearby pit. By jumping into the pit portal, the momentum will "fling" the user through the wall portal and to their destination. A slight variant to this is the "Wedge Fling," where the wall-based portal is instead placed on a upward-slanted, elevated surface for vertical travel as opposed to horizontal travel.[3]

A more complex form of "Flinging" is the "Double Fling," performed when lacking a deep enough pit from which to fling. It is performed in the same manner as flinging, but at a reduced height. In the absence of a pit or tall object to jump from, one portal is placed on the floor instead, while the other is placed on the wall as before. Entering into the floor portal will eject the player from the wall portal. As the player falls, they should move the floor portal below them (if necessary) to "catch" themselves. This portal will fling them through the wall portal with their momentum intact, thereby gaining the needed momentum without the use of a pit.[3]

In the absence of a portal-friendly high wall from which to fling, there is another way to exploit momentum for the purposes of reaching remote ledges: the "Floor-to-Floor" technique. Instead of placing one portal on a high wall, it is instead placed on the floor while the second is placed in a pit. Jumping into the pit ejects the player from the ground-level portal, allowing them to reach a previously unattainable ledge.[3]

The last technique, advised to be mastered by the player who wants to succeed in the Advanced Chambers, is called "Portal Ledge." It involves standing partway through an already deployed portal, and using it as a ledge to reach surfaces beyond the range of the current location. It can literally be used as a ledge to jump through, or another portal can be created from inside it and edge one's way toward a distant destination. The latter technique requires the player to exit out of their original portal immediately after placing the second portal, to prevent them from exiting through it. Creatively utilized in this way, the Portal Ledge enables the player to skip large parts of rooms.[3]

Early model (with visible hands) and early crosshair in an early Test Chamber 13.

The concept of shooting blue and orange portals to solve puzzles was directly imported from Narbacular Drop, whose team was hired by Valve to develop that technology into what became Portal.

The earliest known ASHPD model appeared like a modified Gravity Gun. The prongs directly based on that of the latter[3] are still in the final model.

The ASHPD model seen in the Portal trailer features "F-22" written in black on its top,[4] while concept art shows "A-12." It was replaced in the final model by the word "APERTURE" with under it a barcode and "04/." The end is faded, suggesting more alphanumerics used to come after "04/." This number suggests that the gun used by Chell is model 4 among the gun reserve, or that this model is the fourth version of the gun.

As seen in a very early Portal screenshot, the hands and forearms of the ASHPD user were to be featured in the viewmodel. Chell's right hand and forearm are still present in the final viewmodel, although the texture is broken. However the texture file can still be found in the game files, revealing what may be an early Aperture Science logo, followed by the number "122-7605," possibly an early Test Subject ID. These are not featured in Chell's model, which probably did not (at least fully) exist at that time of the game's development. Although in Portal: Still Alive and the Xbox version of The Orange Box, the texture is fixed, but still no hand at the bottom; just at the back.

Concept art for the final version.

As seen in several early Portal screenshots, a modified Half-Life 2 HUD was first reused.

As seen in the earliest known Portal screenshots, the orange portal was originally purple. The final colors, blue and orange, are actually the same as the ones featured in Narbacular Drop, Portal’s predecessor technically speaking. Before being orange, the orange portal also was more halfway between yellow and orange.

The portals seen in the Portal trailer[4] are slightly different than the retail ones, and have purple waves swirling in the middle.

The firing sound of the ASHPD when it is still attached to its pedestal originally was the charging sound of the Combine Guard Gun, a weapon cut from Half-Life 2.

The "ASHPD" acronym bears a striking resemblance to Adrian Shephard's name (Adrian SHePharD), which led many players to speculate it is a hidden Easter egg, suggesting Shephard's involvement in Portal or its sequel. In addition, completing Portal unlocks a new menu background which contains a keyboard that has all the letters in Adrian Shephard's name highlighted, and these keyboards can also be seen throughout the game. Kim Swift said in an interview that the ASHPD acronym was actually a complete coincidence and that they added the keyboard highlights after people mentioned the acronym.[5] Valve's Doug Lombardi subsequently confirmed the Portal reference as a complete coincidence.[6]

The ASHPD in Portal 2 has new firing sounds (although not dissimilar from the originals), as well as new sounds when something goes through a portal. The portals also give off light in their surroundings.

With the Razer Hydra controller and Sixense DLC for Portal 2 installed, the ASHPD gains several new abilities, similar in function to the Physgun from the Half-Life 2 leak. In addition to its normal ability to pick up objects, it can extend the beam to move them further away from the player, even through portals, up to a distance of several meters away. It can also physically grab and reorient portals from any distance so long as they remain on a flat, acceptable surface for portals. It cannot move them across wall corners. Solid objects grabbed by the beam can be rotated on all three axes, allowing for precision aiming with the Weighted Pivot Cube. There is also a new type of Cube, the Scaling Cube, which can be manipulated by the ASHPD, allowing the user to make it larger and distort its shape. Doing so also changes the physical properties of the cube; making the cube larger, for example, not only increases its size but also its mass, allowing it to break a pane of glass that it normally could not and crush anything it lands on. These features work in both the single-player campaign and the Sixense map pack included with the DLC. Free aim is enabled in co-op, but all other features are disabled.

Typing "impulse 101" in Portal gives all the Half-Life 2 weapons and shows the HUD, where a standing man glyph is used for the ASHPD.

The ASHPD does not work by default in Garry's Mod. Although its prop can be imported with the Portal content, it cannot be spawned as a working portal device, as Garry's Mod does not have the necessary code to make it work. However fan-made working versions are available.

The ASHPD can be used in Half-Life 2 and its episodes and Half-Life: Source by simply copying all the game data of the related game into the Portal data folder, then using the console to load the required map. The Half-Life 2 maps will work seamlessly with the ASHPD and vice versa, partly because of development and system similarity.

When Chell is killed by an Energy Pellet, the ASHPD disintegrates with her.

In Portal 2, the Portal Gun has a walking animation.

In the Portal 2: Valentine's Day, the Portal Device has the portal firing sounds switched over (blue to orange and orange to blue).

According to the Aperture Investment Opportunity #4: Boots video, the ASHPD is powered by a miniature black hole, which is kept stable through the use of a cooling fan at the rear of the device. In case the black hole should begin to fail, two miniature German stick grenades, stored within the casing, can be used to restart it, by screwing them into two small holes in the device. Should the fan fail, the device should be disassembled to retrieve the Event Horizon Estimation Wheel, which will determine the minimum safe distance to survive the resulting overload.

The ASHPD seems to be fairly durable, as one is able to survive the fall into the Incinerator Room and is covered by debris but is still fully functional. The same ASHPD also survives Chell's fall into the old Aperture Science facility, which was approximately 4 kilometres.

In Portal 2, the ASHPD gives off blue energy similar to electricity before it is picked up, indicating it is damaged, but ceases to give off this energy and appears to function normally after being picked up.

A safety poster in the more ancient chambers of Aperture Laboratories features a picture of an earlier model of the ASHPD known as the Aperture Science Portable Quantum Tunneling Device. Judging by its silhouette, it was a massive, backpack reactor with a hose running from the bottom to the "barrel" of the gun, a lot like the Gluon Gun from Half-Life.

When Chell installs GLaDOS to the Portal Device (by stabbing PotatOS onto a prong of the portal device), GLaDOS comments that the gun probably contains magnesium, giving her a voltage boost.

Even though GLaDOS stated to "not submerge the Device in liquid even partially," Chell can still do it via the gels and the clear liquid (presumably water) in Portal 2.